Intra-amniotic infection (IAI) is an important cause of maternal-fetal morbidity. In a previous case-controlled study, we found that quantitative amniotic fluid (AF) cultures from patients with IAI were consistent with a bacterial etiology in 70% of cases. Further, Mycoplasma hominis is isolated significantly more often in AF of these patients than in AF of matched controls (35% vs 8%, p less than .001), and our preliminary serologic studies suggest an important role for M. hominis in the pathogenesis of IAI. In aim 1, we will extend these observations by serologic and blood culturing techniques for M. hominis. Since IAI is a polymicrobial infection, it is difficult to determine by cultures alone which bacterial isolates are, in fact, most important in the disease's pathogenesis. We also propose to determine antibody response to a variety of commonly isolated or high-interest bacterial in the sera of patients with IAI and in controls. Because the microbial etiology is not explained by high virulence bacteria nor by M. hominis in approximately 20% of cases, we also plan to investigate the role of Chlamydia trachomatis by serologic techniques. We have also shown that, compared to AF from controls, AF from patients with IAI is less likely to show bacterial inhibitory activity against an E. coli test organism and has significantly higher mean phosphorus and immunoglobulin G concentrations. It is likely that there is more than one active inhibitory system. In aim 2, we propose to identify the active inhibitory fraction(s) in AF of patients with IAI and in controls. We will investigate the specificity of AF immunoglobulins and will fractionate AF by sequential ultrafiltration to determine what systems are responsible for AF bacterial inhibition in our population. The overal objective of this proposal is to extend our observation on the microbiology and mechanism of IAI. Further understanding may allow improve treatment and prevention of IAI an related early neonatal infections.